This invention relates generally to the field of lasers and more specifically to infrared generation in semiconductor lasers.
Some infrared semiconductor lasers use bipolar injection pumping and are based on narrow band-gap materials such as lead salts. These lasers, however, are usually less robust and less reliable than their shorter-wavelength counterparts based on GaAs or InP. Other infrared semiconductor lasers operate on intersubband, rather than interband transitions and have a unipolar (n-type) design. Intersubband lasers are based on InP or GaAs technology. These lasers, however, suffer from problems stemming from the need to maintain a large population of carriers on a very short-lived excited level. One problem is that a large pumping current may be needed to support laser operation, which may lead to overheating. As a result, these lasers typically operate in a pulsed manner or continuously only if significantly cooled. The second problem is that strong non-resonant losses of the infrared radiation are caused by free-carrier absorption and diffraction, which increase sharply at longer wavelengths. Consequently, it is difficult for semiconductor lasers to overcome losses for wavelengths above approximately 30 microns.
In accordance with the present invention, a method and device for infrared generation are provided that substantially eliminate or reduce the disadvantages and problems associated with previously developed devices and methods.
According to one embodiment of the present invention, infrared generation is disclosed. A first laser field having a first frequency associated with a first interband transition is generated. A second laser field having a second frequency associated with a second interband transition is generated. The generation of the first laser field occurs substantially simultaneously with the generation of the second laser field. A third laser field is generated from the first laser field and the second laser field. The third laser field has a third frequency associated with an intersubband transition. The third frequency is substantially equivalent to a difference between the second frequency and the first frequency.
A technical advantage of one embodiment of the present invention may be that infrared generation is achieved without population inversion on the operating intraband transition. This is achieved with the aid of laser fields simultaneously generated on the interband transitions, which serve as the coherent drive for the frequency down-conversion to the infrared region.
A technical advantage of another embodiment may be that the embodiment employs drive fields that are self-generated in the same laser cavity, instead of using external drive fields. This eliminates problems associated with an external drive such as beam overlap, drive absorption, and spatial inhomogeneity problems.
A technical advantage of another embodiment may be the enhancement of nonlinear wave mixing near a resonance with an intersubband transition. The efficiency of wave mixing increases with approaching resonance inversely proportional to the detuning from resonance and reaches the limiting quantum efficiency corresponding to one infrared photon per one drive field photon.
A technical advantage of another embodiment may be the cancellation of resonance one-photon absorption for the generated infrared radiation due to coherence effects provided by self-generated drive fields. This happens when two-photon stimulated processes prevail over one-photon absorption.
Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims. Embodiments of the invention may include none, some, or all of the technical advantages.